Bipolar snares are known, and examples are given in U.S. Pat. Nos. 4,493,320, 4,905,691 and 5,078,716. Each of these designs have a pair of wires extending from an elongate sheath, the wires being separated by an insulating divider to form first and second bipolar electrodes. An electrosurgical current flows between the wires, cutting the tissue as the wires are drawn into the sheath.
Each of the above designs, however, suffers from difficulties in completing the cutting of tissue as the wires are drawn against the end of the sheath.
U.S. Pat. No. 5,078,716 describes a bipolar snare in which the loop and connector are be received within the sheath. However, when the wires are withdrawn within the sheath there is a risk of the wires becoming twisted resulting in shorting between the wires. This is countered by an additional section of insulation adjacent the connector. This additional insulation prevents shorting between the wires, but results in the less efficient cutting of tissue, especially when the wires are very close to the sheath.
EP047501A illustrates a bipolar snare with a rotatable guide member, but in this device the guide member prevents the whole of the loop including the insulating connector from being withdrawn within the sheath. Thus the cutting effectiveness of the snare device, particularly when the wires are close to the end of the sheath, is reduced.